1. Field of the Invention
The present invention relates to an improvement in a construction process for furnaces having walls which are thermally insulated as a result of the use of refractory fibers, and more specifically to an improvement in the process in which these refractory fibers are installed according to the technique called "blanket on edge".
2. Description of the Prior Art
In this technique, blankets or flexible slabs of ceramic fibers are cut into strips which are subsequently stacked on top of one another, so as to constitute a wall, the thickness of which corresponds to the cut-out outline of the strips and the faces of which are formed by the strip edges stacked on one another.
In furnaces heated with a liquid or gaseous fuel, for example natural gas, heat is supplied by means of burners, these being devices in which there occurs the combustion reaction of the fuel mixed with air providing the oxygen necessary for the reaction. An industrial burner consists of a usually metal part which is located outside the furnace and in which the two fluids (fuel and oxidant) are introduced under the requisite conditions for the reaction and sometimes for their mixing, and of a second part which is called the burner orifice tube or combustion tunnel and in which the combustion reaction takes place.
Because of the temperature stresses to which this orifice tube is subjected, it must both be refractory and have good thermal insulation to maintain at this location the highest possible temperature to ensure good combustion of the fuel/oxidant mixture, whilst at the same time withstanding thermal shock, this last point being the most difficult to achieve.
Since the ideal material has not yet been discovered, most burner orifice tubes are usually made of dense refractory bricks or concrete, this being the best compromise at the present time. the burner, itself located outside the furnace, to the interior of the latter, where the combustion products are released, it is placed in the thickness of the wall, forming an unusual point in it. When the wall is made of ceramic fiber, the burner orifice tubes made of relatively heavy material (concrete or brick) have many sensitive points which are difficult to connect to the rest of the wall and of which the performances as regards stability and insulation vary greatly.
Orifice tubes are sometimes composed of formed pieces made from ceramic fibers molded in a vacuum. However, the results obtained are uneven as regards temperature stresses and stresses both thermal and mechanical (erosion as a result of the velocity of the hot gases) which often exceed the resistance performances of the molded pieces. Moreover, the slightest overheating causes uncontrolled shrinkage cracks, and at length this damages the burner orifice tube because scales and even entire parts of burner blocks become detached.
The object of the invention is to provide a burner orifice tube or combustion tunnel, the thermal properties of which are close to those of the adjacent wall obtained by the technique of "blanket on edge", and which is connected effectively to the latter, but nevertheless has high resistance to the difficult conditions prevailing at the level of a burner.
Another object of the invention is to provide a process for obtaining such a component.